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This list of Frequently Asked Questions addresses mainly corridor mapping of existing power lines and for new lines construction.
Q1. How wide of a corridor can you map?
We are able to map most corridor widths requested by the customer. However, in most of the cases for power line mapping, the corridor width is 100 m centered to the line axis.
Q2. Are there steps that can be taken to improve the accuracy of data points? If so, how does this affect the field operation, price, processing, etc.?
Accuracy of data points is predetermined and based on customer need. It is included in the specifications and agreed with by the customer. The improvement of accuracy does affect the pricing, field operations and processing. We always balance accuracy, reliability and cost.
Q3. What is the effect of having the ground stations closer or further apart?
Generally, the effect of stations positioned closer to one another increases accuracy. However, based on our experience, the positive affect of having the stations closer than approximately 50 km apart becomes insignificant. Several other factors affect spacing decisions and are considered during the planning stage.
Q4. How many passes must you make to collect the necessary data?
In almost all cases, we only require one pass to collect accurate data.
Q5. At what altitude do you typically fly?
Altitude at which we perform the survey flight depends on the specification of the final product we deliver. In general, most of the cases for power line mapping, we fly at an altitude of approximately 250 m above ground level.
Q6. Can LiDAR data be integrated with or replace previously collected Asset Mapping data?
Since LiDAR data is truly georeferenced actual 3D data of assets, it can be integrated with previously collected Asset Mapping Data. To a certain extent, it can also replace previously collected Asset Mapping Data.
Q7. Why it is your methodology using LiDAR better than the traditional ground survey?
LiDAR produces more accurate results in less time and in greater detail than the traditional ground survey method. Our technology enables ground survey and maintenance crews to perform their jobs more effectively and with less time consuming work.
Q8. What is the difference between your methodology using LiDAR and conventional photogrammetry method?
Our survey method using LiDAR increases the accuracy of data, is not affected by vegetation nor affected by the 2D to 3D transformation required by photogrammetry. In addition, our method produces more accurate, detailed 3D maps.
Q10. How do you measure the temperature of the wires?
We use an indirect method to obtain the temperature of the conductors. During the survey, we measure and record such parameters as wind speed, wind direction, solar radiation, and ambient air temperature. In addition, we also obtain line load data from the customer. Combining this information with the physical parameters of the conductors, we calculate the temperature of the conductors applying either CIGRE or IEEE approved methodologies. Verification checks by our customers have proven that this method delivers extremely accurate results. In compared to the direct measurements of the conductor temperature, our indirect method proves to be easier and more productive.
Due to the current IR technology development limitations we cannot use thermo vision cameras to measure the temperature of the wires simultaneously with laser surveys.
Q11. What are potential problems that must be considered during the planning process for a typical LiDAR job?
Although rarely discovered, there could be potential problems associated with survey flights regulations. These will be addressed thoroughly during the preparation stage.
Q12. I have used other LiDAR providers, why is your service better? Are the products the same? Why are your costs lower?
The difference is, we are not LiDAR providers - we are solution providers. Our client base spreads through out 11 countries and, to date, we successfully have conducted more than 25,000 km of overhead power line surveys. Our breadth and depth of customer experience and advanced technology allows us to operate as the most effective and efficient mapping solutions company. Please contact us for more information.
Q13. How do you do your ground control? How far apart are the base stations? How many miles or km can you survey per day on a corridor?
Usually we set up ground control stations using geodetic network trigmarks. For more information on ground stations separation please refer to question 3 (Q3). Daily productivity (km of corridor per survey day) is affected by such factors as line voltage and terrain, specification of the final product, width of a corridor, territory (urban, suburban, farm etc.), and others. Typical example is approximately 200 km of 220 kV line per one survey day.
Q14. On wide area surveys, how many acres or square miles/km can you survey per day? What is the level of accuracy? How does the pricing change depending upon the accuracy of contour maps desires? What about feature extraction pricing?
On wide area surveys we typically cover 40 - 45 sq. km a day subject to terrain conditions, specifications, weather factors, etc. The level of accuracy is based on customer need and determined during the planning stage. Pricing is based on the specifications.
Q15. What is the minimum size job you will perform? (Both corridor and wide area)
We will consider any size of job. As in the case with most contracts, price per unit decreases as volume increases. The mobilization cost becomes minor at approximately 500 km (corridor)/400 sq. km.
Q16. What determines the appropriate laser (5 kHz - 50 kHz) system for the job?
The pulse repetition rate for power line surveys generally affects only the point density. It is the final product specifications that determine the appropriate points density. Equal points densities can be achieved with different systems, starting from 5 kHz to modern 50 kHz. Important factors to consider are that modern 50 kHz systems are higher in capitalization costs (more dollars per operational hour); consume more power, greater in size and weight - which requires bigger (more expensive) helicopters. For power line surveys, the flight speed and altitude above ground level is generally independent of pulse repetition rate of the system. Altitude at which the aircraft flies is limited by the visual tracking of the power line from the pilot's seat - most pilots navigate visually using the monitors and cameras to "fine tune". The average flight speed is affected by curvatures of the lines. It should be also noted that the greater the repetition rate the greater amount of data, which increases post processing time and expense. Realistically, additional points density deliver no additional useful information for the post processing. Considering the above, the optimum pulse repetition rate is between 10 - 20 kHz.
Q17. While I get an orthorectified photo with this LiDAR product? If so, what is the image resolution?
Yes, you will. Typical image resolution on the ground plane is 10 - 15 cm. This value could be amended in accordance with customer's specification.
Q18. What about attribute detail .... Will I be able to determine what type of pole, structure, cross arm configuration, conductor bundles, etc.?
Some attribute details can be determined using LIDAR data and in accordance with the specification. Our asset management services can be used to obtain small details such as conductor bundles types. etc.
Q19. What is the minimum voltage or line size that we can do a sag analysis on? Do you have experience with low voltage single line circuits?
The minimum voltage we have experience with for sag analysis is 60 kV on a single circuit line. Our services can also be used on smaller lines for sag analysis.
Q20. How fast will we get our data back? What is the collection to processing ratio?
Our typical data processing rate is 500 km a month. This can be increased per customer's request.
Q21. Does time of year and weather conditions impact a LiDAR survey? What about snow covered ground? Wetlands?
Time of year and weather conditions does impact days suitable for survey flights. Survey flights can be performed during daylight without strong (over 15 m/sec) wind, no precipitation or smoke. Due to equipment operational limitations, ambient air temperature should remain above approximately -5°. Snow covered ground would affect the accuracy of ground position measurements because the laser will measure the position of the snow cover instead of true ground. Wetlands have similar effect on the measurements - the laser will measure the water and will not penetrate down to the bottom. If the customer is most interested in clearances to the crossing infrastructure, vegetation, towers locations, sags and other parameters other than ground profile, wetlands and snow cover do not affect this data.
Q22. Do you require engineering drawings (as builts) and/or other assistance from us in your planning or operations?
Typically we appreciate any information about the line such as engineering drawings, existing GIS, towers/structures drawings etc.
Q23. Can we provide our own helicopter?
Yes, you can provide your own dedicated helicopter. The most preferable models are Eurocopter EC120B Colibri and Bell-206 JetRanger. To perform the survey in accordance with the specifications, we would have to validate pilot capabilities first. It should be also noted that typically we do not remove and install the equipment till the completion of the survey flights because it affects the calibration of the equipment. It means that once equipment is installed onboard and calibrated, no other job can be performed with the use of the helicopter during the survey flights.
Q24. Can this service be provided by a fixed wing aircraft? What are the options?
For wide area surveys - yes. For existing power line surveys - no. This is because of the difference in motion and extremely limited view of the power line from the pilot's seat in fixed wing aircraft (thus limiting the ability of the pilot to navigate the power line visually). The helicopter model options are as follows: Eurocopter EC120B Colibri, Eurocopter AS350 (AS355), Bell-206 JetRanger (LongRanger), and some other light helicopters.
Q25. Do you propose leasing a local helicopter provider or do you ferry in your own helicopter?
We propose leasing a local helicopter provider. We do not ferry in our own aircraft. To increase efficiency and safety, we always consider using local pilots as the first option.
Q26. How many people are in the aircraft? Do you require a customer representative in the aircraft?
Typically there is a pilot, an observer and an equipment operator onboard. A customer representative can join the crew and act as a flight observer and also provide navigation aid to the pilot and the equipment operator.
Q27. How many people are on the typical field crew? Do you require a customer representative as part of the field crew?
Typically there are five to 15 members of the field crew depending of the complexity of the field works and specification of the final product. We do not require the customer representative as part of the field crew; however we welcome one should the customer require this.
Q28. Do you have a separate mobility cost or is everything built into your per mile/km/wide area pricing?
We can provide a separate mobility cost for smaller jobs, but generally everything is built into our per mile/km/wide area pricing for projects bigger than 500 km / 150 sq. km. Please refer to question 15 (Q15).
Q29. Do we get any software as part of the project? Do we have to purchase any special software to be able to use the LiDAR product most efficiently?
Our LIDAR data is configured and formatted ready to use in any GIS or CAD software (PLS-CADD, AutoCAD, MicroStation, ArcView, etc.). If you use your own software for data management, our product can be formatted to suit your requirements.
Q30. How quickly can we start after contract award?
Typical preparation stage takes approximately 4 weeks after contract award. We do work with customers' time constraints, but in some cases, complexity of project would prolong the preparation stage.
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